Fiber optic cables with extruded access features and methods of making fiber optic cables

ABSTRACT

Cables are constructed with embedded discontinuities in the cable jacket that allow the jacket to be torn to provide access to the cable core. The discontinuities can be longitudinally extending strips of polymer material coextruded in the cable jacket.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/023,051, filed on Sep. 10, 2013, which is a continuation of U.S.patent application Ser. No. 13/845,697, filed on Mar. 18, 2013, which isa continuation of International Application No. PCT/US11/57574, filedOct. 25, 2011, which claims the benefit of priority to U.S. ApplicationNo. 61/407,744, filed Oct. 28, 2010, the content of each which is reliedupon and incorporated herein by reference in its entirety.

BACKGROUND

In order to terminate the fibers within a cable, the fibers must beaccessed within the protective structure that comprises the cablejacket. Access to the cable interior can be difficult if the cable isdesigned to maximize the protection of the fibers within. In most casescable access is achieved through extensive use of sharp cutting toolswhich can be dangerous if handled improperly. In addition to the safetyconcern regarding cable access, additional time during fiber access andtermination increases the cost of installing the cable.

SUMMARY

According to one embodiment, a cable comprises a core and a jacketsurrounding the core. The jacket may be formed primarily from polymericmaterials. The jacket comprises a primary portion of a first material,and at least one discontinuity of a second material. The discontinuityextends along a length of the cable, and allows the jacket to beseparated to provide access to the core. The discontinuity can beembedded within a primary or main portion of the jacket. Thediscontinuity can extend along the entire length of the cable, or forshorter sections of the cable that allow access to particular sectionsof the cable.

According to one aspect, the second material of the discontinuity can bea polymeric material that is extruded in the same process as the firstmaterial of the jacket, which can be formed from a polymeric materialdifferent than that of the second material.

According to another aspect, the second material can be different fromthe first material due to its being subjected to different cureconditions.

According to another aspect, the degree of adhesion between the firstmaterial of the jacket and second material forming the discontinuity canbe selected to provide desired separation properties as well as cablejacket properties. The cohesive strengths of the first material and ofsecond material can also be selected to provide desirable separation andjacket properties.

According to another aspect, the second material can include selectedquantities of the first material to enhance bonding between the maincable jacket portion and the discontinuities.

Those skilled in the art will appreciate the above stated advantages andother advantages and benefits of various additional embodiments readingthe following detailed description with reference to the below-listeddrawing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

According to common practice, the various features of the drawingsdiscussed below are not necessarily drawn to scale. Dimensions ofvarious features and elements in the drawings may be expanded or reducedto more clearly illustrate the embodiments of the invention.

FIG. 1 is a cross-section of a fiber optic cable according to a firstembodiment.

FIG. 2A is a cross-section of the cable jacket illustrated in FIG. 1.

FIG. 2B is an isolated view of a portion of the cable jacket taken onsection line 2B in FIG. 2A.

FIG. 2C is a perspective view of a section of the cable jacketillustrated in FIG. 2A.

FIG. 3 illustrates various adhesion ratios.

FIG. 4A is a cross-section of a cable jacket according to a secondembodiment.

FIG. 4B is an isolated view of a portion of the cable jacket taken onsection line 4B in FIG. 4A.

FIG. 4C is a perspective view of a section of the cable jacketillustrated in FIG. 4A.

DETAILED DESCRIPTION

FIG. 1 is a cross-sectional view of a fiber optic cable 110 according toa first embodiment. The cable 110 has an optically conductive core 120,a first and a second strength component 130, and a cable jacket 140. Thefirst and second strength components 130 are disposed on opposite sidesof the optical fiber 120 and have axial centerlines 134. The core 120can comprise, for example, one or more optical fibers. In theillustrated embodiment, the core 120 is a single optical fiber. The core120 also has an axial centerline (not illustrated) located at the centerof its cross-section that may be generally aligned with the axialcenterlines 134 of the strength components 130 along a common plane A-A.The orientation of the strength components 130 on the common plane A-Ain part provides preferential bend characteristics to the fiber opticcable 110. The axial centerlines of the core 120 or fibers in the cable110 need not be exactly aligned with the plane passing through the axialcenterlines of the strength components 130, and may move off of theplane, e.g. “up” and “down”, with respect to the strength components 130along the length of the cable 110. For the purposes of thisspecification, when the fiber or fibers of a cable are said to be“generally aligned with” or “aligned with” a plane passing through twostrength components, it is understood that the fiber may be slightlyoffset from that plane, for example, by 0.5 millimeters in eitherdirection. The jacket 140 can be formed primarily from polymermaterials, and can be generally referred to as “polymeric.” In thisspecification, the term “polymer” and “polymeric” include materials suchas, for examples, copolymers, and polymer materials including additivessuch as fillers.

In the exemplary embodiment shown in FIG. 2, the cable jacket 140envelops and may contact the optical fiber 120 and also envelops and maycontact both strength components 130. The cable jacket 140 has a medialheight MH which is measured as the jacket height or thickness in amedial or center region 146 of the cable cross-section, the medialregion 146 being the portion of the jacket 140 located between thestrength members 130. The medial height MH may also be defined as theheight of the cable at the centerline of the optical fiber or group ofoptical fibers, or the height at a longitudinal bisection plane of thecable 110. The medial height MH may be measured between flat orrelatively flat opposed medial surfaces 148 of the medial region 146,extending above and below the core 120. An end or total height EH of thecable jacket 140 is measured as the thickness of the jacket 140 at endportions 150 of the cable cross-section, extending above and below thecenterline of each strength component 130. In the exemplary embodiments,the end height EH corresponds to the total height of the cable. In theexemplary embodiment, the end portions 150 extend outwardly from themedial region 146 in generally circular cross-sections. Quantities ofadhesion promoter 154 may be included on the strength components 130 topromote bonding with the cable jacket 140. As illustrated, the adhesionpromoters disclosed in this specification and in the figures appear toseparate the cable jackets from the strength components. For thepurposes of this specification, a strength component is considered to be“in contact” with a cable jacket if an adhesion promoter is interposedbetween the strength component and the cable jacket to promote bondingtherebetween.

The cross-sectional footprint 160, or cross-sectional area, of the fiberoptic cable 110 may be substantially smaller than the cross-sectionalfootprints of conventional fiber optic cables of the same type. The areaof the cross-sectional footprint 160 may be less than about 25millimeters squared, for example. According to one embodiment, the areaof the cross-sectional footprint 160 is in the range of 8 millimeterssquared to 22 millimeters squared. According to another embodiment, thearea of the cross-sectional footprint 160 is in the range of 10millimeters squared to 18 millimeters squared. The area AJ of thepolymeric material forming the jacket 140 can be less than 13millimeters squared. In the illustrated embodiment, the medial height MHis less than the end height EH at the strength components 130. Relief orrecessed portions 158 in the cable jacket 140 are included to reducestresses on the fiber in the core 120 in order to preserve opticalperformance, as discussed in further detail below. The height ratio forthe cable 110 is defined as the ratio of the medial height MH to the endheight EH, or MH/EH. According to one embodiment of the invention, theheight ratio is less than 0.95, in the range of 0.5-0.95. The exemplarycable 110 has an overall width W in the range of about 3-6 millimeters.The radii R1 of the end portions 150 can be in the range of about 1-2millimeters. The radii R2 of the strength components 130 can be in therange of about 0.35-0.9 millimeters. The separation distance S1 of thestrength member axes 134 can be in the range of about 1.9-2.6millimeters.

According to one aspect of the present embodiment, the jacket 140includes a separation feature that facilitates access to the core 120.In the exemplary embodiment, the separation feature is a pair ofdiscontinuities 180 that extend along the length of the cable 110, withone discontinuity located above the core 120 and one located below thecore 120. The discontinuities 180 enable easier separation of the jacket140 in the vicinity of the core 120, so that the jacket 140 can bepulled apart along the centerline of the cable 110. The core 120 andfiber(s) located therein are therefore easily accessed by bisecting thecable along fracture lines formed at the discontinuities 180. In thisspecification, the term “discontinuity” indicates a portion of thejacket 140 of different, second material composition than a primaryportion 184 or first material of the jacket 140. The primary portion 184of the jacket 140 can essentially be a unitary extruded polymer coatingsurrounding, embedding, and contacting the core 120, the strengthcomponents 130, and the discontinuities 180. The primary portion 184also extends between the strength components 130 and the core 120. Thediscontinuities 180 extend longitudinally through the primary portion184 along a selected length of the cable 110. Discontinuities extendingalong the entire length of the cable 110 are effective in providingaccess to the core 120. Shorter discontinuity lengths may also beeffective however. For example, discontinuities having lengths of atleast 10 centimeters along the length of the cable may be sufficient.

In the exemplary embodiment, the discontinuities 180 are bonded to theprimary portion 184 of the jacket 140 when the jacket is extruded. Theprimary portion 184 and the discontinuities 180 can be formed fromextrudable polymers, so that as the extrudates used to form the primaryportion 184 and the discontinuities 180 cool and solidify, theextrudates become bonded to a desired degree. When the discontinuities180 are formed while extruding the primary portion 184 of the jacket,the bond between discontinuity 180 and the remainder of the jacket 140can be generally described as enabled by polymer chain entanglement asthe jacket 140 solidifies. The degree of bonding between the primaryjacket portion and the material within the discontinuity 180, thecohesion of the primary and second materials, and the shape of thediscontinuity 180 can be selected to provide desirable separationproperties at the discontinuities 180. The jacket 140 can accordinglycomprise a cohesive, unitary, composite polymeric structure. Theinterfaces between the primary portion 184 and the discontinuities 180can include transition regions between the materials of the primaryportion 184 and the discontinuities 180. A discontinuity can be extrudedinto the primary portion 184 of the jacket 140 at any location where apoint of access might be formed. In the illustrated embodiment, thediscontinuities 180 are closely spaced from the core 120, and bothdiscontinuities 180 are wholly embedded or surrounded by the primaryportion 184 of the jacket 140. In alternative embodiments,discontinuities can extend to the outer perimeter of a cable jacket orto the outer perimeter of the core.

As shown in FIG. 1, the discontinuities 180 can be relatively narrowstrips in the jacket 140, and may occupy relatively small portions ofthe jacket cross-sectional area AJ. For example, the discontinuities 180can have cross-sectional areas A_(D) that are less than 10% of AJ, andas low as less than 5% of AJ. In the illustrated embodiment, thediscontinuities 180 each have cross-sectional areas A_(D) that are lessthan 2% of AJ. In FIG. 1, two discontinuities 180 are formed in thejacket 140 to facilitate opening of the jacket 140. Depending on theform that the core 120 takes, the number, spacing, shape, compositionand other aspects of the discontinuities 180 can be varied. For example,a single discontinuity in the jacket 140 may be sufficient to allow thecable jacket 140 to be opened away from the core 120.

FIGS. 2A-2C illustrate the discontinuities 180 in greater detail. FIG.2B is an isolated view of one of the discontinuities 180 in the jacket140. Referring to FIG. 2B, a discontinuity 180 can have a maximum widthA, a height B, and a center spacing from the core 120 of D. The distancefrom the top surface of the cable to the core 120 is C. According to oneaspect, the aspect ratio A:B is in the range of 1:4 to 1:100. Ingeneral, lower aspect ratios A:B, which indicates narrowerdiscontinuities, are favorable in cable cross-sections as shown in FIGS.2A-2C. It is these discontinuities that allow for a stress concentrationto develop at the root of a discontinuity and thus initiate failure ofthe primary jacket material. The illustrated ratio B:C is about 1:2,which indicates that the height of a discontinuity is about half of thejacket thickness between the core and the top, central portion of thejacket. The ratio B:C is selected to provide ease of access to the coreand to maintain sufficient robustness of the cable 110, and will varywith factors such as the fracture toughness of the material of theprimary portion 184, the bond between the discontinuities 180 and theprimary portion 184, and other factors. According to one embodiment, theratio B:C is at least 1:4, or, stated alternatively, B is at least ¼ ofthe jacket thickness C at the centerline of the cable.

The ratio of the adhesion strength between the first material of theprimary portion 184 and the second material of the discontinuities 180is also a factor in determining the shape and compositiondiscontinuities. The ratio of the second material cohesive strength tothe adhesion strength between the first and second materials (Ratio A)can be in the range of, for example, 1:20 to 20:1. FIG. 3 illustratesvarious adhesion ratios. With a secondary cohesive discontinuity 180strength to adhesion strength of 1:20, there is very little cohesivestrength within the second material compared to the adhesion between thetwo materials and thus failure will take place within the secondmaterial. A ratio of 20:1 indicates a relatively strong cohesive secondmaterial compared to the adhesive bond between the materials and thusfailure will take place at the interface between the primary portion 184and the discontinuity 180. In the illustrated embodiment, the adhesionratio is at least 4:1. It is the failure of the material or bond thatallows for a sufficient stress concentration to develop at the tip ofthe discontinuity 180 and thus initiate failure of the first material.The ratio of the first material strength to the adhesion between thefirst and the second material (ratio B) can be, for example, in therange of 20:1 and 400:1. Ratio B in the range of 1:1 and 20:1 willfollow a linear relationship with ratio A in the range of ratio A statedabove.

The materials and processes used to form the primary portion 184 and thediscontinuities 180 can be selected for relatively easy access to thecore 120 by tearing the jacket 140. The cable 110 may be constructed tomeet other requirements for robustness, such as requirements for thejacket 140 stay intact under tensile loads, twisting, in temperaturevariations, and when subjected to other known cable test criteria, suchas, for example, ICEA 460, and GR20. In the illustrated embodiment, theprimary portion 184 in the illustrated jacket 140 is extruded frommedium density polyethylene (MDPE), and the discontinuities 180 areextruded from a second material primarily of polypropylene (PP). Thejacket 140 is formed in a coextrusion process so that the primaryportion 184 and the discontinuities 180 bond during cooling to formrelatively strong bonds. The cable jacket 140 can be robust yetrelatively low pull forces are sufficient to shear or tear the jacket140 along the discontinuities 180. Without being bound by theory,Applicants believe the bond between polypropylene of the discontinuityand polyethylene of the main portion can be created by adding selectedquantities of ethylene compounded in the polypropylene discontinuity.The quantities of polyethylene in the discontinuity 180 are believed tobond with the polyethylene of the primary portion 184, as well asresulting in molecular entanglement between the polyethylene andpolypropylene. According to this understanding, the amount of ethylenein the polypropylene extrudate used to form the discontinuities 180 canbe increased to increase the bond between the discontinuities and theremainder of the jacket 140.

In general, if the primary portion 184 is formed from a first extrudedpolymer material, and the discontinuities 180 are formed from a secondextruded polymer material, the discontinuities can include from 0.5%-20% by weight of the first polymer material. One embodiment of a thinfilm discontinuity contains PP with about 9% PE. Higher PE contents,such as to up 20% PE, are also possible. PE contents of less than 0.2%in PP may result in insufficient bonding between the main portion and adiscontinuity. In one embodiment, the first polymer material iscomprised of at least eighty per cent by weight of a first polymer, andthe second extruded polymeric material is comprised of at least seventyper cent by weight of a second polymer and at least 0.5 per cent byweight of the first polymer. In this embodiment, the first polymer canbe PE and the second polymer can be PP.

Coextrusion of the discontinuities 180 and the main portion 184 can beachieved by adapting a conventional extrusion head such as is used tofrom the cables disclosed in PCT App. No. PCT/US2009/058017. Theextrusion head is adapted by adding one or more apertures through theextrusion head that allow the introduction of a second, molten extrudatematerial into the molten first extrudate used to form the first portion184 of the jacket 140. The first and second extrudate materials areallowed to cool and solidify together and to achieve a desired degree ofbonding between the first portion and the discontinuities. According tothe present embodiment, the first and second extrudate materials can beintroduced into and extruded through a common extrusion head so thatdiscontinuities and the first jacket portion are coextruded at the samelocation.

FIGS. 4A-4C illustrate an alternative, annular jacket 440 according to asecond embodiment. The jacket 440 is suitable for use in roundcross-section cables similar to those disclosed in U.S. Prov. App. No.61/330,038. The jacket 440 includes two discontinuities 480 that can beused as breach locations where the jacket 440 can be separated from acable core as shown in U.S. Prov. App. No. 61/330,038, from an armor, orfrom another component of a cable. The primary portion 484 of the jacket440 can essentially be a unitary extruded polymer coating in which thediscontinuities 480 are wholly embedded.

In the exemplary embodiment, the discontinuities 480 are bonded to theprimary portion 484 of the jacket 440 when the jacket is extruded. Theprimary portion 484 and the discontinuities 480 can be formed fromextrudable polymers, so that as the two extrudate materials used to formthe primary portion 484 and the discontinuities 480 cool and solidify,the extrudates become bonded to a desired degree. When thediscontinuities 480 are formed while extruding the primary portion 484of the jacket, the bond between the discontinuity 480 and the remainderof the jacket 440 can be generally described as enabled by polymer chainentanglement as the jacket 440 solidifies. The degree of bonding can beselected to provide desirable separation properties at thediscontinuities 480. The jacket 440 can accordingly comprise a cohesive,unitary, composite polymeric structure. A discontinuity can be extrudedinto the primary portion 484 of the jacket 440 at any location where apoint of access might be formed. In the illustrated embodiment, thediscontinuities 480 are located on opposite sides of the annular jacket440 to that the jacket can be torn in half and pulled away. Bothdiscontinuities 480 are wholly embedded or surrounded by the primaryportion 484 of the jacket 440.

As shown in FIG. 4A, the discontinuities 480 can be relatively narrowstrips in the jacket 440, and may occupy relatively small portions ofthe jacket cross-sectional area AJ. For example, the discontinuities 480can have cross-sectional areas AD that are less than 10% of AJ, and aslow as less than 5% of AJ. In the illustrated embodiment, thediscontinuities 480 each have cross-sectional areas AD that are lessthan 2% of AJ.

Referring to FIG. 4B, a discontinuity 480 can have a maximum width A, aheight B, and a center spacing from an inner edge of the jacket 440 ofD. The thickness of the jacket 440 is C. According to one aspect, theaspect ratio A:B is in the range of 1:4 to 1:100. In general, loweraspect ratios A:B, which indicates narrower discontinuities, arefavorable. The illustrated ratio B:C is about 2:3, which indicates thatthe height of a discontinuity is about 2/3 of the jacket thickness. Theratio B:C is selected to provide ease of access to the core and tomaintain sufficient robustness of the cable 410, and will vary withfactors such as the fracture toughness of the material of the primaryportion 484, the bond between the discontinuities 480, and otherfactors. According to one embodiment, the ratio B:C is at least 1:3, or,stated alternatively, B is at least 1/3 of the jacket thickness C.

In the illustrated embodiment, the primary portion 484 in theillustrated jacket 440 is extruded from medium density polyethylene(MDPE), and the discontinuities 480 are extruded from a materialprimarily comprised of polypropylene (PP) with small amounts of MDPEcompounded therein. The jacket 440 was formed in a coextrusion processso that the primary portion 484 and the discontinuities 480 bondedduring cooling to form relatively strong bonds. The cable jacket 440 isrobust yet relatively low pull forces are sufficient to shear the jacket440 along the discontinuities 480.

Coextrusion of the discontinuities 480 and the main portion 484 can beachieved by adapting a conventional extrusion head. The extrusion headis adapted by adding one or more apertures through the extrusion headthat allow the introduction of a second, molten extrudate material intothe molten first extrudate used to form the primary portion 484 of thejacket 440. The first and second extrudate materials are allowed to cooland solidify together and to achieve a desired degree of bonding betweenprimary portion and discontinuity. According to the present embodiment,the first and second extrudate materials can be introduced into andextruded through a common extrusion head.

The cable jacket primary portions and the discontinuities described inthis specification can be made from various polymer materials. Eitherprimary portion or discontinuity may be made from polypropylene (PP),polyethylene (PE), or blends of materials such as a blend of PE andethylene vinyl acetate (EVA), flame-retardant material such asflame-retardant polyethylene, flame-retardant polypropylene, polyvinylchloride (PVC), or polyvinylidene fluoride PVDF, filled materials suchas polybutylene terephthalate (PBT), a polycarbonate and/or apolyethylene (PE) material and/or an ethylene vinyl acrylate (EVA) orother blends thereof having fillers like a chalk, talc, or the like, andother materials such as a UV-curable acrylates.

The terms “polymer” and “polymeric” as used in this specificationindicate extrudable materials consisting primarily of polymers, butallows for the inclusion of filler materials, for example.

In general, the desirable separation properties disclosed in thisspecification may be obtained by coextruding the discontinuities from adifferent material than the material used to form the primary portion ofthe jacket. As an alternative method, the discontinuities may be madefrom the same material as the remainder of the jacket, but subjected todifferent curing conditions, for example.

Many modifications and other embodiments, within the scope of the claimswill be apparent to those skilled in the art. For instance, the conceptsof the present invention can be used with any suitable fiber optic cabledesign and/or method of manufacture. Thus, it is intended that thisinvention covers these modifications and embodiments as well those alsoapparent to those skilled in the art.

What is claimed is:
 1. A cable, comprising: a core comprising at leastone optical fiber; and a jacket surrounding the core, the jacketcomprising: a primary portion of a first material; and a discontinuityof a second material wholly embedded in the primary portion, thediscontinuity extending along a length of the cable, wherein the firstand second materials are extrudable, the first material being differentfrom the second material.
 2. The cable of claim 1, wherein the firstmaterial is polymeric and wherein the second material is polymeric. 3.The cable of claim 2, wherein the first material is comprised of atleast eighty percent by weight of a first polymer, and wherein thesecond material is comprised of at least seventy percent by weight of asecond polymer and at least 0.5 percent by weight of the first polymer.4. The cable of claim 2, wherein the first material is different fromthe second material due to being subjected to different cure conditions.5. The cable of claim 1, wherein an inner surface of the jacket contactsthe core.
 6. The cable of claim 5, wherein the core comprises a singleoptical fiber.
 7. The cable of claim 1, wherein the core comprises aplurality of optical fibers.
 8. The cable of claim 1, wherein a heightof the discontinuity is greater than a width of the discontinuity. 9.The cable of claim 1, wherein the discontinuity has a length of at least10 centimeters along the length of the cable, wherein a cross-sectionalarea of the discontinuity is less than 10% of a cross-sectional area ofthe jacket.
 10. The cable of claim 1, further comprising: a firststrength member on a first side of the core; a second strength member ona second side of the core; and wherein the jacket surrounds and contactsthe core, the first strength member and the second strength member. 11.The cable of claim 1, wherein a height of the discontinuity is at leastone third of a distance between an inner surface of the jacket and aclosest exterior edge of the jacket.
 12. The cable of claim 11, whereina height of the discontinuity is less than the distance between an innersurface of the jacket and the closest exterior edge of the jacket.
 13. Acable, comprising: a core comprising at least one optical fiber; and ajacket surrounding the core, the jacket comprising: a primary portion ofa first extrudable polymer material; and a discontinuity surrounded bythe primary portion such that a first section of the primary portion islocated between the discontinuity and an exterior surface of the jacketand a second section of the primary portion is located between thediscontinuity and the core, wherein the discontinuity is formed from asecond extrudable polymer material different than the first extrudablepolymer material, wherein the discontinuity extends along a length ofthe cable.
 14. The cable of claim 13, further comprising a seconddiscontinuity, wherein the jacket is an annular jacket, wherein thediscontinuities are located on opposite sides of the annular jacket. 15.The cable of claim 13, wherein a height of the discontinuity is greaterthan a width of the discontinuity.
 16. The cable of claim 15, whereinthe height of the discontinuity is at least one third of a distancebetween an inner surface of the jacket and a closest exterior edge ofthe jacket.
 17. The cable of claim 16, wherein the height of thediscontinuity is less than the distance between an inner surface of thejacket and the closest exterior edge of the jacket, wherein thediscontinuity has a length of at least 10 centimeters along the lengthof the cable
 18. The cable of claim 13, wherein the discontinuityextends along the entire length of the cable, and wherein across-sectional area of the discontinuity is less than 5% of across-sectional area of the jacket.
 19. The cable of claim 13, whereinthe first extrudable polymer material is comprised of at least eightypercent by weight of a first polymer, and wherein the second extrudablepolymer material is comprised of at least seventy percent by weight of asecond polymer and at least 0.5 percent by weight of the first polymer.20. A cable, comprising: a core comprising at least one optical fiber;and a jacket surrounding the core, the jacket comprising: a primaryportion of a first polymer material; and at least two discontinuities ofa second polymer material located within in the primary portion, eachdiscontinuity extending a length of at least 10 centimeters along thelength of the cable, wherein the first polymer material is differentfrom the second polymer material, wherein a height of each of the atleast two discontinuities is less than a distance between an innersurface of the jacket and a closest exterior edge of the jacket.